Typically, a power transmission device is, at a self-propelled vehicle such as a motorcycle or a four-wheel buggy car, provided for transmitting drive force generated by an engine (a motor) to a drive wheel. The power transmission device is, while being connected or disconnected to/from the crankshaft, a mechanical device configured to change the number of rotations of a crankshaft of the engine to transmit the number of rotations to the drive wheel, and mainly includes a clutch and a transmission.
The clutch described herein is a mechanical device configured to transmit rotary drive force of the crankshaft of the engine to a transmission side while being connected or disconnected to/from the crankshaft. Moreover, the transmission is a mechanical device configured to change the number of rotations of the crankshaft of the engine by a plurality of gear stages formed by a combination of a plurality of gears, thereby transmitting the number of rotations to a drive wheel side.
In this case, the clutch is configured to selectively switch between transmission and blocking of rotary drive force from the engine in such a manner that a clutch drive unit including an electric motor drives a push rod to move back and forth. For example, a clutch actuator as a clutch drive unit disclosed in Patent Literature 1 described below includes an assist spring configured to assist rotary drive force of a clutch motor.